Wireless telecommunications is a rapidly expanding part of the telecommunications industry. For example, there is a rapidly increasing demand for, and an increasing number of subscribers to, the services of the so-called cellular telecommunication networks by which those cellular subscribers can call other parties via radio communications links to the cellular networks. Cellular subscribers can not only call other cellular subscribers but they can also be given access to conventional public switched telephone networks for making telephone calls to other parties subscribing to the telephone services provided by those telephone networks. There is no need for a physical connection between the cellular subscriber and the party being called. Telephone calls involving moving parties--for example, those traveling in automobiles and other forms of transport--thus are made possible by cellular telecommunications networks and systems.
Cellular telecommunications networks comprise a plurality of base stations for communicating via radio with cellular subscribers located in predetermined geographical areas served by the base stations. The geographical area served by a base station is called a cell. Each base station communicates with subscribers located in its cell via one of a number of communications resources, which, in a frequency division multiple access (FDMA) arrangement, may be one of a number of carrier frequencies modulated by a cellular subscriber and the base station. A plurality of subscribers may be able to use the same carrier frequency in a time division multiplex arrangement, known as time division multiplex access (TDMA), whereby subscribers are assigned certain time slots during which they transmit and receive on the assigned carrier frequencies. Yet another method by which subscribers may communicate by radio with base stations involves spread spectrum code division multiple access (CDMA) techniques. Combinations of these methods may also be used. In response to requests from subscribers, the base stations assign one communications resource, for example, a frequency and/or time slot, or a CDMA sequence, not currently being used to each requesting subscriber. The assigned communications resource then is used by the cellular subscriber to communicate with the base station and with a called party.
Requests for assignment of communications resources in a cellular telecommunications network can occur in a variety of ways. For example, a request for assignment of resources can result from a cellular subscriber initiating a telephone call to another party or responding to a telephone call which has made to the cellular subscriber. A particularly important occurrence requiring a communications resource assignment is a handoff of a mobile cellular subscriber already engaged in an ongoing telephone call from one base station to another base station due to movement of the subscriber from one cell to another cell.
As the number of subscribers to cellular telecommunications services has increased, a trend which is already dramatically evident and is expected to continue in the future, it has become increasingly difficult to provide adequate service for normal voice transmission, much less for other services such as data transmission. This is due to the fact that there are only a finite number of communications resources for which an increasing number of subscribers must contend. To alleviate the problem of availability of a limited number of communications resources, it has been proposed to divide existing cells into smaller cells, called microcells, and to increase the amount of frequency reuse in nonadjacent cells and microcells, thus accommodating a greater number of subscribers with the same number of communications resources. As the number of subscribers increases in any given cellular telecommunications network, however, there will be an increasing number of resource assignments which must be made and, therefore, there will be an increasing need to make fast resource assignments in that network. More importantly, in the case of dense microcellular network environments, where the geographical areas served by each transmitter and receiver becomes smaller, shorter movements of a mobile cellular subscriber connected to the network need even faster resource assignments because frequent handoff operations are required.
In addition to addressing the need to utilize a limited number of communications resources to meet the needs of increasing number of subscribers in dense microcellular environments, it also would be advantageous to more efficiently use the limited communications spectrum allotted to the cellular network. In specific terms, it would be particularly advantageous if silent periods between talk spurts during voice transmissions of one subscriber could be used by another subscriber for a voice transmission or could be used for some other purpose such as facsimile or data transmission. In this regard, techniques such as voice activated resource sharing have been proposed, but these cannot now be used because resource assignments are not fast enough in current cellular networks. Finally, it would be advantageous to provide different levels of service for at least some cellular subscribers.
Currently, some of the commonly used techniques for communications resource assignment in radio based telecommunications are statistical in nature. Among these are techniques known as ALOHA, slotted ALOHA, and packet reservation multiple access (PRMA). Resource utilization and throughput are unsatisfactory with such techniques because of collisions between competing subscribers, particularly under heavy traffic conditions which are expected in microcellular environments. Collisions result in none of the contending subscribers obtaining service which thereby wastes communications resources and increases the amount of time it takes for a subscriber to obtain a communications resource assignment, which seriously hinders handoff operations, especially in microcellular environments. Techniques such as voice activated resource sharing clearly cannot be used with current resource assignment techniques used in existing cellular networks and thus available resources cannot be used as efficiently as they might be used if resource assignments could be made more rapidly.
Accordingly, there is a need for a communications resource assignment technique which is rapid enough to adequately serve a large number of fast moving cellular subscribers densely positioned in a region served by a wireless telecommunications network. In addition, there is a need to efficiently utilize the limited communication resources available in a wireless telecommunications network.